The various elements can be organized into families with similar chemical properties. This organization is made evident in the periodic table. Learn more about the periodic table and about the individual elements through this entertaining set of videos.

Stars come in very different sizes. Only the most massive stars end their lives as supernovas. And among those, the huge ones leave behind a neutron star after they explode as supernovas, and the really huge ones leave behind a black hole. Most stars are too small to become supernovas and end their lives as white dwarfs. Here is a good introduction to the life cycles of stars.

Even the shortest lived stars last for a million years. An average star like our Sun lasts for many billions of years. But humans have only been observing the heavens with telescopes for four hundred years - meaning that we haven’t been watching any one star long enough to see it evolve. So how do we know how a star goes through its life? The answer is that by observing millions of stars that are at different stages of their lives, we have been able to deduce the full life cycle of a star as well as why different stars go through different stages. The Hertzsprung-Russell diagram captures information about our observations of stars in such a way that helps astronomers think about how stars evolve.

Of course, the matter this lesson discusses is visible matter, which only makes up about 4% of the matter of the universe. What comprises the rest? Dark matter and dark energy. Check out these TED-Ed Lessons to find out more about dark matter and dark energy:
-Dark matter: The matter we can't see
-Dark matter: How does it explain a star's speed?
-Shedding light on dark matter

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